1. Field of the Invention
The present invention is in the field of optical devices and specifically relates to apparatus for projecting, viewing and editing motion picture film.
2. The Prior Art
The shortcomings of conventional intermittent movement projection devices are well known. Complex mechanisms are needed to synchronize the intermittent movement pull-down claw, shutter and sprocket wheels. This results in a complicated, expensive and noisy machine. Loops and additional sprocket wheels are needed to isolate the sound reading devices from the intermittent movement to produce adequate sound quality. Slow speed orientation produces flicker due to the shutter. Special and complex shutters and movements are needed to compensate for frame rate discrepancies when film-to-video projection is desired. Film that is worn or badly spliced can be easily damaged by the intermittent movement. High speed and reverse operation is hazardous. The machines are heavy to carry and mechanical breakdowns are not infrequent.
To remedy these shortcomings, continuous movement devices have long been sought after. The most successful of these are optical rectification systems using rotating prisms to refract light to compensate for the moving film and thereby to produce stable projected images. However, these devices are not without their own complications. Very few of them are in present use.
Solid or plane-parallel plate prisms are described in the following U.S. Pat. Nos. 2,441,013, to Ehrenhaft, issued May 4, 1948; 2,508,789, to Harrison, issued May 23, 1950; 3,155,979, to Mast, issued Nov. 3, 1964; 3,259,448, to Whitley et al., issued July 5, 1966; 2,325,131, to Harrison, issued July 27, 1943; 3,563,643, to Jeney, issued Feb. 16, 1971. In Nos. 2,508,789; 3,155,979 and 3,563,643 gearing is used to synchronize the movement of the film and prism. This gearing is expensive, complicated and noisy and causes backlash which produces unstable images.
Attempts to eliminate gearing are shown in U.S. Pat. Nos. 2,259,448 and 2,441,013. But these systems require complicated light paths, aperture plates, additional optical components, and awkward and bulky mechanisms. Also, the amount of refraction produced by solid prisms is limited by the index of refraction of the material used. Providing high quality multifaceted solid prisms is quite costly and troublesome. Moreover, the results from these devices as seen on a projection screen is a wiping effect between successive film frames producing unstable images at low speeds, and varying illumination causing annoying and fatiguing light flicker.
To achieve high quality flickerless images, various schemes using hollow prisms have been described in the following U.S. Pat. Nos. 2,817,995, to Kirkham, issued Dec. 31, 1957; 2,972,280 to Kudar, issued Feb. 21, 1961; 3,539,251, to Husted et al., issued Nov. 10, 1970. These prisms are of the "isotransport" design-- the sprocket carrying the film and the prism are joined and thereby rotate in unison, eliminating the need for gears or other linkages. These systems succeed in providing a true "lap-dissolve" transition between successive film frames. Picture images are therefore stable at low speeds of projection and flicker is eliminated.
In U.S. Pat. Nos. 2,817,995 and 2,972,280 the light rays travel through the walls of the prisms twice. Because one wall is close to the film plane, any dirt or scratches on it would have a noticeably adverse effect on the image quality. Moreover, these prisms also have complicated means to adjust the length of the light path to compensate for film shrinkage and manufacturing irregularities. These devices are composed of a plurality of refractive elements, increasing the likelihood of optical aberrations, necessitating the precise alignment of each element and causing the system to be expensive. Furthermore, these designs do not permit a central axle or shaft to be passed through the prism as desired.
In U.S. Pat. No. 3,539,251 the light travels through only one wall of the prism. However, since the facets of this prism are on its outer circumference, the light rays must travel in a step-shaped path for proper optical rectification. (If they were to travel in a U-shaped path, the image of the moving film would be doubly unstabilized.) Because of this no central shaft may be passed through this system either. Consequently, sprocket teeth must be mounted to the prism side of the film and cannot be mounted on the other edge of the film or both edges as may be desired. Importantly, no means are disclosed for adjusting the length of the light path from film plane to prism to compensate for film shrinkage and to avoid the necessity for the precise manufacture and assembly of the prism system.
French Pat. No. 768,714 issued Aug. 11, 1934 to Askania-Werke A. G. discloses an optical rectification device comprising a number of preferably spherical lenses disposed in a ring. Because the lenses are formed at their edges, a shutter is required. This in turn produces flicker. The film is disposed in a plane, and no means are disclosed for relating the movement of the film to the movement of the other parts.
Two basic kinds of motion picture sound projectors are discussed in this application. The first includes those machines designed to project picture film with a sound track encoded on it. The sound track is usually optically printed on the edge of the film or magnetically encoded on a magnetic stripe on the edge of the film. In either case, the sound accompanies the film with the synchronization point of the sound usually displaced ahead of the picture synchronization point. This displacement was originally designed to accommodate the film to prior art cameras and sound projectors and varies according to the width of the film and whether the sound is optically or magnetically encloded. For example, in 16 mm film with an optical sound track, the sound precedes the appropriate picture by 26 frames. This sound-on-picture-film is called "composite" film, and the projectors designed to show this film are called "composite" projectors.
Composite projectors include consumer, audio-visual and professional machines designed for front-screen projection and rear-screen projection. They may be reel-to-reel loaded, manually threaded, "self-threaded", cartridge loaded, etc.
U.S. Pat. Nos. 1,979,718 to Wehr, issued Nov. 6, 1934 and 2,095,848 to Wittel, issued Oct. 12, 1937 describe prior art composite projectors. Since an intermittent film movement creates objectionable sound "flutter", some means are necessary in these machines to cause the film to be continuously moving as it passes over the sound reader. The mechanisms necessary to accomplish this involve complicated arrangements of intermittent film pull-down mechanisms which are linked to one or more continuous rotating sprocket wheels, usually by multiple gears and/or timing belts. Machines employing such mechanisms tend to be relatively complicated, expensive, noisy and heavy. Due to their larger number of moving parts, they are easily subject to mechanical breakdown and require skilled technicians for repairs. Their projected pictures flicker at low speeds because of the shutters necessary for the intermittent movement, while projection at high speeds is hazardous to film due to the fast-moving intermittent pull-down mechanisms. Threading film on these machines, often done by non-technical people such as consumers, teachers, business persons, etc., is complex and time-consuming.
The second kind of projectors are "interlock" projectors, normally used in professional and audio-visual applications. These machines are built to project a picture film and simultaneously and in synchronization to play sound from one or more separate magnetic sound films.
An example of a machine which plays one separate sound film is the "Sonorex 16/16 Interlock Projector" distributed by Arriflex Company of America, Cat. No. 253-100. This machine is basically a conventional intermittent projector on one side and a mechanically interlocked sound film player on the other side. Only one sound track can be played at a time.
To play more than one sound film, prior art systems are limited to individual sound reproducing machines synchronized to each other and to a separate projector usually by electronic motor control means. While these "dubbing" systems are useful for professional sound mixing, they are indeed expensive to rent or purchase and inconvenient to use when it is desired only to view a film with separate sound tracks.
In the past, most editing has been done on "upright Moviola-type" editing machines, such as are described in U.S. Pat. Nos. 1,873,341 to Serrurier, issued Aug. 23, 1932 and 1,921,469 to Kuhn et al., issued Aug. 8, 1933. These machines have an intermittent film advance movement which is noisy, mechanically troublesome and which can cause damage to the film. Additionally, this type of movement makes it difficult to achieve good sound quality. These machines were originally designed to accommodate short lengths of picture film and are not adequate by today's standards to handle multiple tracks of long rolls of synchronized picture and sound film.
Some contemporary "flatbed" editors such as described in U.S. Pat. Nos. 3,856,389 to Gardner, issued Dec. 24, 1974 and 3,912,383 to Stutz, issued Oct. 14, 1975 have continuous (non-intermittent) film advance movements and allow for the handling of long rolls of multiple tracks of picture and sound film. However, these machines are relatively expensive, are mechanically very complex, and due to their large size and weight cannot be carried by a single individual nor transported in a standard size automobile.
A third category of editing machines comprises various types of motorized sychronizers with attached viewers, such as are described in the following U.S. Pat. Nos. 3,427,099, to Marsden, issued Feb. 11, 1969; 3,602,606, to Rigby, issued Aug. 31, 1971; 3,771,860, to Stone et al., issued Nov. 13, 1973, and British Pat. No. 1,016,927, to Hopwood et al., published Jan. 12, 1966. While these machines may be much lower in price and more portable than flatbed machines, they are very slow in operation, do not provide means for automated film feed and take-up, do not have individually and independently clutchable sprocket wheels, and produce low quality sound, and low quality pictures.
Minimizing the size and cost of professional editing machines has become an objective or more and more importance in recent years. There has been a great increase in films made independently in small offices or in people's homes as well as those made on location or elsewhere outside the studio. The large size and weight of flatbed machines have made it impossible, as a practical matter, for one individual to transport such a machine to an office, home, or temporary location. In more permanent editing facilities, such as in studios, rental editing room centers, and film schools, the numerous machines present in one location furthers the need for space-saving machines.
Among the features of the prior art flatbed machines which have contributed to their present limitations from the standpoint of their lack of portability, their complexity and their inconvenience to persons operating them, is their disposition of the film sprocket wheels and feed and take-up plates in the same plane. Thus, as may be seen in U.S. Pat. Nos. 3,856,389 and 3,912,383, considerable surface on the top of the machine is taken up by the film feed and take-up plates which are mounted adjacent one another in the same plane on the table. Any flatbed machine with, for example, one picture and two sound tracks would necessarily require a considerable surface area on its top. Moreover, such a disposition of the film feed and take-up plates makes it difficult for the operator to reach all of the plates to place or remove rolls of film. In addition, such a disposition of sprocket wheels, each with its own axis of rotation, has required separate driving motors and electronic interlock devices, or interconnecting timing belts or gears and electro-magnetic clutches and brakes, to selectively drive the sprocket wheels individually or in synchronization. Such mechanisms are expensive and result in the increase of weight, complexity and likelihood of breakdown of these machines. These devices must normally be maintained and repaired only by trained service persons. There is a great need, especially in non-studio locations for a machine which is simple, reliable and largely serviceable by the editor himself.
The disposition of the film sprocket wheels in the same horizontal plane on the flatbed machines also occupies table space, which limits the working counter space available for the editor's spicing machine, additional rolls of film, film leader, note pads, etc.